Refining fatty acids



3,052,701 Patented Sept. 4, 1962 3,052,701 REFINING FATTY ACS Burt L.Hampton, Port St. Joe, Fla., assignor to The Glidden Company, Cleveland,Ohio, a corporation of Ohio No Drawing. Filed Nov. 12, 1959, Ser. No.852,232 1 Claim. (Cl. 260-419) This invention relates to a process forrefining unsaturated fatty acids. The invention relates moreparticularly to an improved method for treating mixtures comprisingmostly unsaturated fatty acids to improve their color and heatstability. Reference will be made hereinafter mostly to the treatment oftall oil fatty acids although this should not be construed as alimitation of the process of this invention. Examples will be offeredshowing treatment of other fatty acids such as soya oil, cottonseed oil,etc. in accordance with the teachings herein.

Tall oil is made from black liquor soap, a product of the sulfate papermills. The soap skimmings from the mill contain about 60% solids andyields about 50 to 56% of tall oil upon acidulation.

Crude tall oil has a disagreeable odor. This odor generally can beimproved for example by heating and blowing with steam or an inert gas,but some of the ingredients of the tall oil decompose upon standing andthe oil again develops a disagreeable odor.

The viscosity of tall oil varies with the percent rosin acids whichrange from 37% to about 55%. Tall oil has a very wide variation inproperties depending on the source, care in acidulation, etc. Tall oilgenerally made throughout the southern United States has the followingvariations in properties:

Acid number 150-174 Saponification number 160-178 Rosin acids percent 38-5 3 Fatty acids do 3 8-5 3 Unsaponifiables do 6.5-10

In recent years the industry has developed eflicient fractionating unitsfor the separation of rosin and fatty acids. The initial step infractionation is to separate the volatile fraction of crude oil from thenon-volatile or pitch. This first step in a continuous system is carriedout in a flash tower, the volatile fraction being fed to a fractionatingcolumn which separates rosin from the bottom and fatty acids andunsaponifiables from the upper plates. A third column can also beutilized to further remove rosin and unsaponifiables from the fattyacids. Even in the most efficient systems, however, all of theimpurities which contribute to poor color, heat-stability, and poor odorcannot be removed completely. Commercial grades of tall oil fatty acidstherefore, contain from 0.3% to 6% rosin acids and from 0.3% to 4%unsaponifiables.

The nature of the bodies that contribute to poor color and poorheat-stability is not known, but it is suspected that unsaponifiableswhich consist largely of phenolic bodies, alcohols and unsaturatedhydrocarbons are responsible.

In commercial practice in order to obtain a finished fatty acid ofaround Gardner 3 color (1933 Gardner Standard) it is necessary torefractionate more highly colored acids or to remove a much largeroverhead or first fraction cut. Either way results in the loss of largequantities of C-18 fatty acids to a lower grade product giving a pooreconomical picture. Thus, prolonged fractionation in a blocked operationresults in a Gardner 3-4 colored fatty acid containing about 0.5% rosinacids and about 0.5% unsaponifiables. However, even this product haspoor heat-stability. By heat-stability I mean the ability of the fattyacid composition to retain a light color when subjected to a temperatureof 205 C. for a period of one hour. There is no standard heat-stabilitytest adopted by the industry, but one test generally used is as follows:Add fatty acids to a 1 x 8" test tube and immerse in an oil bath at 205C. Adjust the level of the acids to the level of the oil bath. After onehour remove from the bath, cool, fill a Gardner color tube and read thecolor on a Gardner Comparator (1933 varnish scale). This is the testreferred to in this work. The following table records the originalGardner color and color after this test of different commerciallyavailable tall oil fatty acids which will be identified throughout thisspecification as A, B, C, etc. Other analytical data is recorded forcomparison.

TABLE I Commercial Color Color Rosin Unsaps.,

Tall Oil Before After Acid N o Acids, Percent Fatty Acid Heat Test TestPercent 'It is evident from the table that even though a tall oil fattyacid may have a fairly good initial color, the color does not stand upvery well when the acids are subjected to the heat-test. For many usesgood heat-stability is a prerequisite.

It is well known that manufacturers of fatty acids have strived toimprove the color, odor and heat-stability of fatty acid products. Forexample, fatty acids. and vegetable oils have been bleached with naturalabsorbents such as fullers earth and activated absorbents such as thesub-bentonite type clays. Fullers earth is by far the most Widely usedof natural occurring unactivated clays. This mineral is chiefly amagnesium aluminum silicate present in attapulgite and montmorillonite.Fullers earth usually has a pH in the range of 6.5-7.5.

Most raw clays show some ability to decolorize oils and most of thesecan be improved to some extent by acid treatment. However, only a fewtypes can be activated by acid treatment to produce eflicientadsorbents. The types usually used for activation are bentonrites,consisting chiefly of montmorillonite clay minerals. Activated clays andthe art of making them are old in the art. Activation is accomplished bytreating a slurry of clay and water with a mineral acid such ashydrochloric or sulfuric in an amount of about 35% of the total dryweight of the clay. The mixture is then treated with steam to atemperature of about 200 to 210 F. for a period of about 5 to 6 hoursand is thereafter washed and filtered. The teachings of US. Patents1,397,113, 1,642,871, 1,776,990 and 1,796,799 are incorporated herein byreference. Patent 1,776,990 relates to the acid activation ofsub-bentonite type clays and the example presented therein isillustrative of the method used for the preparation of the acidactivated clays applicable to the process herein described. Reference isalso made to Kirk and Othmer, Encylopedia of Chemical Technology, vol.4, p. 55 (1954), for a further description of acid activated clays.

In decolorizing oil by the contact process, the finely ground adsorbentis intimately mixed with the oil to be processed, and the slurry isheated to the desired temperature until adsorption is complete. Thedecolorized oil is separated from the clay by filtration, and the filtercake is washed and steamed to recover oil soakage. The used adsorbent isdiscarded; recovery of contact grade clay seldom being practiced.Although acid-activated adsorbents are more expensive than naturalclays, they usually exhibit much greater decolorizing power, which makestheir use economical. Examples of acid activated clays that can beprepared according to the prior art referred to are the various gradesof commercially available trademarked products such as Filtrol and TheBennett-Clark clays. The Filtrol trademark identifies a group ofacid-activated adsorbents and catalysts from the mineralmontmorillonite,

The acid-activated materials are supplied as fine white powders, 85-95%passing through a ZOO-mesh screen. The examples presented belowillustrate the use of these acid activated adsorbents and will bereferred to as acidactivated crystalline clay(s) or simply as clay(s).

In working toward the improved process of this invention I found thatclays, especially the activated clays were the only practical substancesfor this purpose. More specifically acidic crystalline clay minerals ofa pH of from about 2 to 7.5 are applicable herein. I found that it ispossible to decolorize tall oil fatty acids to a Gardner 2 color orbetter if a sufiicient amount of clay is used. However, this type ofdecolorized fatty acid has poor heat-stability. For example, thecommercial tall oil fatty acid designated as B above, color to 6, can bedecolorized to a 2 to 3 color by stirring with 2% of an acid-activatedcrystalline clay for one hour at 90 C. The tall oil fatty aciddesignated D of a color 3 to 4, when subjected to the same treatment didnot decolorize, and the heat-stability tests showed little improvementon both products. The following table compares:

When 4% acid activated crystalline clay is used to decolorize the abovefatty acids, a 1 to 2 colored product can be obtained but theheat-stability is still poor, yielding around a 7 to 8 color product.

Accordingly, an object of the present invention is to refine fatty acidsto improve their color and heat-stability.

A further object of this invention is to improve the color andheat-stability of distilled tall oil fatty acids. Distilled tall oil maycontain relatively large amounts of rosin acids ranging from 15-65%,while tall oil fatty acids now commercially produced may contain fromtraces of rosin acids up to about 6%. p A still further object of thisinvention is to refine other fatty acids such as those from soybean oil,corn oil, cottonseed oil, and the like to improve the color andheatstability of these mixtures of fatty acids.

A still further object of this invention is to improve the odor of thetall oil fatty acids. Such products, some more than others, have adisagreeable odor representing cation color of 5-6 (Gardner).

a slight carry over from the foul smelling crude tall oil from whichthey are manufactured.

In accordance with the objects of my invention above, I have found thatwhen fatty acids are first treated with a crystalline clay mineral, andthen distilled, the distilled products are reduced in color and improvedin heat stability. Thus in Table 11 above, when the treated fatty acidsB and D are distilled, the color is reduced to 1 to 2 from 3 to 4 andthe heat-stability tests degrade the products only to a 3 to 4 color inboth instances.

It is well known that acids and oils that have been in storage for sometime, may be only a few days, do not decolorize with clays as readily asoils that have been freshly prepared. This difliculty is overcome in thecase of fatty acids by my new distillation after clay-treating step.Thus an old acid which has absorbed a small amount of oxygen can be claytreated, showing little or no improvement in color, but if the productis distilled, both the color and heat stability are greatly improved.

Most of the experimental work described herein was performed, employingthe commercial tall oil fatty acid, designated as B above. An analysisof this fatty acid is as follows: Acid No. 196-l97.8; rosin acids,percent, 0.8-1.4; unsaponifiables, percent, 0.8-1.5; iodine value,133-135; color 5-6 (Gardner 1933 Standards).

The procedures for carrying out these laboratory experiments was to heatabout 500 grams of the fatty acids to the desired temperatures in al-liter, 3-neck round bottom flask fitted with a stirrer, a thermometerand a nitrogen gas inlet tube. The desired amount of clay was then addedall at once and the mixture stirred vigorously for the desired time. Theclay was then removed by filtration using a Buchner funnel at atemperature not greater than around C. The filtrate was then distilledat 1-3 mm. absolute pressure (a range of from 1 to 25 mm. can be used)with no fractionation. To insure removal of most of the volatile acids aflame was played over the top of the flask toward the end of thedistillation.

Example 1 Table III below records an experiment on a relatively freshsample of fatty acid B, that is the sample was only about 24 hours oldwhen used after taking from a regular plant sampling connection. Thissample had the specifi- The Gardner color was 8-9 after the heat-testdescribed above. The sample was treated with 2% of an acid-activatedcrystalline clay for .the specific time at 90 C.

TABLE III Color Color Color Time In Minutes After After Heat Color ofAfter Heat Filtering Test On Distillate Test On Filtrate Distillate Goodinitial color is had rather quickly, but there is some improvement byallowing the reaction to continue. It will be noted that theheat-stability appears to be poorer after the longer period of heating,but the distilled product is superior to the product obtained after theshorter period.

By distillation alone, without clay, the color of the tall oil fattyacid is improved very little, color 5-6.

Example 2 Table IV below records the results using tall oil fatty acid Band different percentages of an acid-activated crystalline clay atdiflerent temperatures.

Table IV Color Color Clay, Color of Fil- Color of Dist. Experi- Per-Temp., Time, of Filtrate of After ment cent C. Mins. trate After Dist.Heat- Heat- Test Test NOTE-Experiment 19 Week old tall oil fatty acid,color 6; experiment 20 fresh tall oil fatty acid, color 5-6.

Example 3 A fresh sample of tall oil fatty acids having a color of 8-9,acid number 196, unsapo-nifiables 0.66%, rosin acids 1.4% (500 grams),was treated with 3% of an acid-activated crystalline clay at 90 C. for60 minutes. After filtering, the color was 5-6, with a heat stability of9-10. The distillate had a color of 2-3. The heat-stability test yieldeda color of 4-5. Distillation alone of the original sample yielded acolor of 5-6.

Table V records the results of refining tests on commercial tall :oilfatty acids designated as D, E, and F above. See Table I for propertiesof these acids.

Two 500 gram samples of tall oil fatty acid B, Gardner color 6 werestirred with 2% each of two different grades of an acid activatedcrystalline clay at 90 C. for 30 minutes. After filtering the sampleswere distilled. Exactly the same results were obtained with each sample:Color after filtering, 3-4 color after heat-stability test 8. Colorafter distilling l-2; color after heat-stability ttest 3-4.

Example 5 Tall oil fatty acid B, color 5-6 (500 grams), was stirredunder nitrogen at 90 C. for 30 minutes with 4% of fullers earth. Thecolor after filtering was 4-5; color after the heat-stability test 8-9.The color after distilling was 3-4; color after the heat-stability testwas 4-5.

Example 6 Five hundred grams of tall oil fatty acid B was stirred with1.6% of an acid-activated clay and 0.4% of Nori-te A, a commercialdecolorizing carbon, at 90 C. for 1 hour. The color of the fatty acidsafter filtering was 3-4; color after the heat-stability test 6. Thecolor after distilling was 2-3; color after the heat-stability test 3-4.

Example 7 Crude tall oil is fed to a column and the pitch removed bysimple flash =dis't1llation. The volatile fraction sample used in thisexperiment had the following analysis. Acid No. 181; rosin acidsunsaponifiables 6%; Gardner color 10-11. This sample was treated with 2%clay as above at 90 C. for 20 minutes. The color of the filtrate was9-10 with a heat-stability color of 12; the original material had aheat-stability color of 12-13. The distillate after clay treating had acolor of 8-9 and a color after heat-stability test of 9.

Example 8 Distilled tall oil is a product normally made as more or lessof a by-product in the fractionation of tall oil. Plant sidestrearndistilled tall oil (in this case) usually contains about 25 to 30% rosinacids and about 1.5% unsaponifiables, the remainder being fatty acids. Asample of this material with the following analysis: Rosin acids 27%,acid number 190, unsaponifia-bles 1.4%, Gardner color 7-8, was treatedwith 2% acid-activated crystalline clay at 90 C. for 20 minutes. Theproduct after filtering had a color of 5-6 with a color after theheatstability test of 8-9. The original sample had a color after theheat-stability test of 9-10. The distilled fitrate had a color of 4-5and a color after the heat-stability test of 5-6. The odor wasconsiderably improved. In all of these examples, the color referred tois Gardner color, 1933 Gardner Standard.

Example 9 An old sample of a double distilled cottonseed oil fatty acidoriginal Gardner color of 1-3 had colored to 4-5. On a straightdistillation with no fractionation the color improved to 0-1 with acolor after the heat-stability test of 4-5. On treating the original oldsample with 2% acid-activated crystalline clay at 90 C. for 30 minutesand filtering, there was no improvement in color. The distillate had acolor of 0-1 with a color after the heatstability test of 3-4. The onlyimprovement here then by treating with clay Was an improvedheat-stability on the distilled product.

Example 10 In this experiment crude tall oil fatty acids were claytreated. The crude tall oil fatty acids of this sample 45 contained 5.2%unsaponifiables and 1.6% rosin acids.

after the heat-stability test of 12-13.

5 test.

7 stability test.

The color was 8-9; color after the heat-stability test 13-14, and theacid number 190. One sample was treated with 2% of an acid-activatedcrystalline clay at C. for one hour. The filtrate had a color of 8-9with a color The distillate had a color of 6-7 with a color after theheat-stability test of 7-8. A second sample treated in the same way with4% clay and filtered had a color of 8-9 and a color after theheat-stability test of 11-12. The distillate had a color of 6-7 and acolor after the heat-stability test of 8.

Example 11 PART A A sample (400 grams) of distilled cottonseed oil fattyacids of Gardner color 6-7 with a color of 12-13 after theheat-stability test; AN. 202 was distilled at 1-2 mm. absolute pressure.The distillate had an acid number of 204, a color of 2-3 and a color of5 after the heat-stability Yield 97.4%.

PART B A 500 gram sample of the same cottonseed oil fatty acids wasstirred with 2% acid activated crystalline clay at 90 C. for one hourand filtered. The filtrate had a color of 5-6 and a color of 9-10 afterthe heat-stability test. A sample (400 grams) of the filtrate wasdistilled at 1-2 mm. absolute pressure. The distillate had an A.N. of206, a color of 2 and a color of 4 after the heat- Yield 97.6%.

Example 12 PART A A sample (400 grams) of distilled soya oil fatty acidsof Gardner color 4-5; color after heat-stability test 10-11; AN. 200,was distilled at 1-2 mm. absolute pressure. the distillate had an acidnumber of 202, Gardner color 1-2 and a color of 5 after theheat-stability test. Yield 97.5%.

PART B A 500 gram sample of soya oil fatty acids (as in part A) wasstirred with a 2% acid-activated crystalline clay at 90 C. for 1 hourand filtered. The filtrate had a color of 4-5 and a color of 8-9 afterthe heat-stability test. A portion of the filtrate (400 g.) wasdistilled at 12 mm. absolute pressure. The distillate had an acid numberof 203, a Gardner color of 1 and a color of 3-4 after the heat-stabilitytest. Yield 97.4%.

The results of the above Examples 11 and 12 show that a clay treatmentfollowed by a distillation yields more highly refined soya or cottonseedoil fatty acid than either a clay treatment or a distillation alone.Products of an improved color and improved heat stability are obtained.

From the foregoing experiments it can also be seen that the claybleaching alone of tall oil fatty acids can improve the color, but theacids have poor heat stability. Furthermore, in cases where there is noimprovement of color by clay-bleaching alone I can obtain a product ofboth improved color and improved heat stability by the process of myinvention which includes a final distillation. There is some evidencethat freshly made fatty acids do bleach more readily with clay, but bythe process of my invention I can use a fatty acid that has been instorage for days, weeks or even months and still obtain very goodresults.

I can use as little as 0.2% clay if activated, and as much as 20%. Froma practical economic standpoint, however, I prefer to use from 0.5% to4%. The amount is not critical.

I have found that a somewhat elevated temperature is better and yields afinal distillation product of good heat stability. However, theconditions are not critical and I can operate at temperatures whichinvolve cooling, say from 0 C.'to 25 C. A preferred temperature is from50 C. to 110 C. although I can employ temperatures of up to 150 C. Ihave found that at 150 C. I obtain an improved product, but I alsoobtain a 6% yield of non-volatile residue. At preferred temperature thenonvolatile residue amounts to only 1 to 1.5% which is about the same asin a blank distillation. I can treat the products from minutes at thehigher temperatures to 24 hours at lower temperatures, but prefer from30 minutes to 3 hours at 50 C. to 110 C.

Practically I desire to use from 0.5 to 4% of an acidactivatedcrsytalline clay in carrying out the process of this invention, aspreviously mentioned, but it should be pointed out that in addition toactivated bentonites other clay-like materials such as glauconite,nontornite, beidellitic clays, halloysite, and some kaolinitic clayshave been successfully acid activated but the relative efliciencies ofthe products are not equal to those obtained from highgrade-sub-bentonites in which the clay mineral montmorillonitepredominates.

Analytical results, including infrared anaylsis, indicate there are nosignificant changes in the products resulting from the treatment of myinvention. The acid numbers, percent unsaponifiables, percent rosinacids remain approximately the same, within experimental error, as thoseof the starting materials.

The acid number possibly tends to be slightly higher and theunsaponifiables slightly lower, but from a practical standpoint there islitlte change.

However, it is obvious that some changes have occurred not measurable byour standard methods of analysis except that in some cases the iodinenumber is lowered by 23 units and the conjugated diene reduced about 1%.It is apparently necessary to remove only traces of certain types ofmaterial to improve color and heat-stability.

Beds of granular clays can be used, instead of stirring with powderedclays.

From the foregoing experimental part it is seen that I have achieved allof the objects of this invention. By treating tall oil fatty acids withclay and distilling, I have obtained a product of better color andbetter heat-stability than by clay treating alone. By the process ofthis invention I can make a fatty acid product of a color of 2 (Gardner)or a color no higher than the original color, or better after theheat-test by treating with clay and distilling. Treating with clayalone, as noted, does not result in a product of good heat-stability andthe color depends on the age of the sample, etc.

I have achieved the same results with fatty acids containing highpercentages of rosin acids and unsaponifiables.

The odor of all products is better after clay treatment, but stillimproved considerably by the final distillation.

Having thus described my invention I claim:

An improved process for upgrading a tall oil fatty acid distillatefraction without substantially changing the com position of saidfraction which consists essentially of suspending in said fraction /24%of finely-divided, acidactivated montmorillonite clay solids, agitatingthe resulting suspension for /2-3 hours at 501l0 C., filterablyseparating said suspension into clay solids and filtrate, distillingsaid filtrate and collecting the resulting redistillate of improvedheat-stable color.

References Cited in the file of this patent UNITED STATES PATENTS

1. AN IMPROVED PROCESS FOR UPGRADING A TALL OIL FATTY ACID DISTILLATEFRACTION WITHOUT SUBSTANTIALLY CHANGING THE COMPOSITION OF SAID FRACTIONWHICH CONSISTS ESSENTIALLY OF SUSPENDING IN SAID FRACTION 1/2-4% OFFINELY-DIVIDED, ACIDACTIVATED MONTMORILLONITE CLAY SOLIDS, AGITATING THERESULTING SUSPENSION FOR 1/2-3 HOURS AT 50*-110*C., FILTERABLYSEPARATING SAID SUSPENSION INTO CLAY SOLIDS AND FILTRATE, DISOF IMPROVEDHEAT-STABLE COLOR.